KR20010103980A - Manufacturing method for lithium secondary cell - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a lithium secondary battery, comprising: (a) an anode precursor and a cathode precursor by applying an electrode composition including an electrode active material, a polymer binder, a conductive agent and a casting solvent, and containing no plasticizer to a current collector; Preparing a; (b) coating a separator precursor by coating a slurry containing a vinylidene fluoride (VdF) / hexafluoropropylene (HFP) copolymer, a plasticizer, an inorganic filler and a coating solvent on both sides of the porous polymer film which is not gelled by the electrolyte solution. Manufacturing; (c) laminating the electrode precursor and the separator precursor to prepare a battery precursor; And (d) injecting an electrolyte solution into the battery precursor to activate the lithium secondary battery. The method of manufacturing a lithium secondary battery according to the present invention enables the production of a lithium secondary battery without a plasticizer extraction process by an organic solvent, thereby preventing environmental pollution problems due to the extraction process, and lowering the manufacturing cost of the battery. There is this.

Description

Manufacturing method for lithium secondary battery {Manufacturing method for lithium secondary cell}

The present invention relates to a method for producing a lithium secondary battery, and more particularly, to a method for producing a lithium secondary battery without a plasticizer extraction step by an organic solvent.

Non-aqueous lithium secondary batteries generally comprise an anode, a lithium electrolyte prepared from a lithium salt dissolved in one or more organic solvents, and a cathode of an electrochemically active material, which is typically a chalcogenide of a transition metal. During discharge, lithium ions from the anode travel through the liquid electrolyte to the electrochemically active material of the cathode that absorbs lithium ions while releasing electrical energy. During charging, the flow of ions is reversed so that lithium ions exit the electrochemical cathode active material and are plated back into the lithium anode through the electrolyte. Non-aqueous lithium secondary batteries are disclosed in US Pat. Nos. 4,472,487, 4,668,595, 5,028,500, 5,441,830, 5,460,904, and 5,540,741.

To address the problem of dendrite and sponge lithium growth, lithium metal anodes were replaced with carbon anodes such as coke or graphite in which lithium ions were intercalated to form Li _x C ₆ . When such a cell is operating, lithium moves out of the carbon anode, as in a cell with a lithium metal anode, to the cathode where lithium is absorbed through the electrolyte. During recharging, lithium returns to the anode and is inserted back into the carbon. Since there is no lithium metal present in the cell, the anode does not melt even under severe conditions. In addition, no dendrite and sponge lithium growth occurs because lithium is not plated but is reintegrated into the anode by insertion.

Recently, lithium secondary batteries have emerged that use a porous polymer matrix as a separator, and it has been demonstrated that conductivity can be improved by using a porous polymer matrix. One method of making such a porous polymer matrix includes preparing a polymer structure containing a plasticizer, such as dibutyl phthalate, and removing the plasticizer to form voids in the polymer. The plasticizer may be included in the lithium secondary battery at less than about 50 weights before it is removed. Current methods of removing such solvents are extraction with other organic liquid solvents such as dimethylether, methanol and cyclohexane. In general, in the assembly of a lithium secondary battery, an electrolyte solution containing an electrolyte solvent and a salt is added to activate the lithium secondary battery precursor after removing the plasticizer.

As described above, although the lithium secondary battery manufactured using the plasticizer has excellent electrochemical operation ability, the solvent used for extracting the plasticizer is a harmful organic solvent, which causes a problem of environmental problems. In addition, there is a problem of increasing the manufacturing cost of the lithium secondary battery by lengthening the production process time and decreasing the production yield by going through the extraction step. In the technical field to which the present invention pertains, studies have been made on a method for producing a more economical and stable lithium secondary battery, in particular, without a plasticizer extraction process.

Accordingly, the technical problem to be achieved by the present invention is to provide a method for producing a lithium secondary battery without a plasticizer extraction step by an organic solvent.

In order to achieve the above technical problem, the present invention,

(a) preparing an anode precursor and a cathode precursor by applying an electrode composition including an electrode active material, a polymer binder, a conductive agent, and a casting solvent, and not including a plasticizer, to a current collector;

(b) coating a separator precursor by coating a slurry containing a vinylidene fluoride (VdF) / hexafluoropropylene (HFP) copolymer, a plasticizer, an inorganic filler and a coating solvent on both sides of the porous polymer film which is not gelled by the electrolyte solution. Manufacturing;

(c) laminating the electrode precursor and the separator precursor to prepare a battery precursor; And

(d) providing a method of manufacturing a lithium secondary battery, comprising the step of activating by injecting an electrolyte solution into the battery precursor.

In the method of manufacturing a lithium secondary battery according to the present invention, it is preferable that the battery precursor has a bicell structure in which a cathode precursor, a separator precursor, an anode precursor, a separator precursor, and a cathode precursor are sequentially stacked.

In the method of manufacturing a lithium secondary battery according to the present invention, it is preferable that the electrode composition further comprises an alcohol solvent selected from the group consisting of methanol, ethanol, isopropanol and mixtures thereof.

In the method of manufacturing a lithium secondary battery according to the present invention, it is preferable that the porous polymer film not gelled by the electrolyte solution is a porous polyethylene film in which a porous polyethylene film or a porous polypropylene film is laminated on both sides.

In the method of manufacturing a lithium secondary battery according to the present invention, the plasticizer is ethylene carbonate, propylene carbonate, dimethyl carbonate, diethoxyethane, dibutyl phthalate, dimethoxyethane, diethyl carbonate, dipropyl carbonate and mixtures thereof It is preferably any one selected from the group consisting of.

In the method of manufacturing a lithium secondary battery according to the present invention, the vinylidene fluoride / hexafluoropropylene copolymer is preferably coated to have a thickness of 1 to 50㎛.

Before describing the present invention in detail, terms will be defined as follows.

The term "cell precursor" refers to a cell prior to being activated, and generally such a cell precursor includes an anode precursor, a cathode precursor and a separator precursor. In addition, the term "activation" means impregnating a non-aqueous organic solvent and an electrolyte solution of a lithium compound that emits lithium ions in the solvent into the battery precursor. After activation, the battery is charged by an external energy source before use.

The term "unit cell" generally refers to a composite containing an anode, a cathode, and a separator, which contains a nonaqueous organic solvent and an electrolyte comprising a lithium compound which produces lithium ions in the solvent, the composite comprising A structure in which the structure is located in the order of cathode, separator, anode, separator, and cathode is called "bicell structure". The term "cell" also refers to two or more unit cells that are suitably connected in series / parallel to provide the required operating voltage and current levels.

Hereinafter, a method of manufacturing a lithium unit secondary battery according to the present invention will be described in detail.

In general, a method of manufacturing a lithium secondary battery may be divided into an anode precursor manufacturing step, a cathode precursor manufacturing step, a separator precursor manufacturing step, a battery precursor manufacturing step, and an activation step, which will be described accordingly.

1. Preparation of Anode Precursor

The anode precursor is prepared by dissolving the polymer binder in a casting solvent, separately adding the above solution to a mixture obtained by dry mixing the anode active material and the conductive agent, and uniformly mixing to prepare an anode composition, which is cast on an anode current collector. It is then formed by drying.

In addition, the anode composition may further include any one alcohol solvent selected from the group consisting of methanol, ethanol, isopropanol and mixtures thereof. Here, the alcohol solvent is insoluble in the polymer binder, but is mixed with the casting solvent, and is removed during the subsequent drying process to form pores in the anode precursor.

The mixing volume ratio of the alcohol solvent and the casting solvent is preferably 1: 3. If the mixing volume ratio of the casting solvent to the alcohol solvent exceeds the above range, the porosity characteristic in the finally obtained anode precursor is poor, and if the mixing volume ratio of the casting solvent is less than the above range, obtaining an anode composition having a uniform composition is obtained. It is not preferable because it is difficult to uniformly cast this composition onto the current collector itself.

As the anode active material, the conductive agent, the polymer binder, and the casting solvent, a material commonly used for the purpose in the art to which the present invention pertains may be used. For example, carbon, graphite, or the like can be used as the anode active material. In addition, carbon black is used as the conductive agent, and at least one selected from fluorine-based polymers such as polyvinyl alcohol, methyl cellulose, carboxymethyl cellulose, polyethylene glycol and polyvinylidene fluoride is used as the polymer binder. N-methyl-2-pyrrolidone, acetone or mixtures thereof can be used.

As the anode current collector, an expanded metal, a punched metal, and a foil made of copper is used.

2. Preparation of Cathode Precursor

The cathode precursor is prepared by dissolving a polymer binder in a casting solvent, separately adding the above solution to a mixture obtained by dry mixing a cathode active material and a conductive agent, and uniformly mixing to prepare a cathode composition, which is cast on a cathode current collector. It is then formed by drying.

In addition, the cathode composition may further include any one alcohol solvent selected from the group consisting of methanol, ethanol, isopropanol and mixtures thereof. Herein, the alcohol solvent is almost insoluble in the polymer binder, but is mixed with the casting solvent, and is removed during the subsequent drying process to form pores in the cathode precursor.

The mixing volume ratio of the alcohol solvent and the casting solvent is preferably 1: 3. If the mixing volume ratio of the casting solvent to the alcohol solvent exceeds the above range, the porosity characteristic in the finally obtained cathode precursor is poor, and if the mixing volume ratio of the casting solvent is less than the above range, obtaining a cathode composition having a uniform composition is obtained. It is not preferable because it is difficult to uniformly cast this composition onto the current collector itself.

The cathode active material, the conductive agent, the polymer binder, and the casting solvent may use a material that is commonly used in the art to which the present invention pertains. For example, LiMn ₂ O ₄ , LiNiO ₂ , LiCoO _2, etc. may be used as the positive electrode active material, carbon black or the like is used as the conductive agent, and polyvinyl alcohol, methyl cellulose, carboxymethyl cellulose, polyethylene glycol as the polymer binder. And at least one selected from fluorine-based polymers such as polyvinylidene fluoride and the like, and N-methyl-2-pyrrolidone, acetone or a mixture thereof may be used as the casting solvent.

As the cathode current collector, an expanded metal, a punched metal, and a foil made of aluminum is used.

3. Preparation of Separator Precursor

The separator precursor is prepared by coating a slurry including a vinylidene fluoride / hexafluoropropylene copolymer, a plasticizer, an inorganic filler, and a coating solvent on both surfaces of a porous polymer film which is not gelled by an electrolyte solution and then drying at room temperature.

The porous polymer film which is not gelled by the electrolyte may be used without limitation as long as it is well known in the art, such as nylon and polyolefin film, but is a porous polyethylene film having a porous polyethylene film or a porous polypropylene film laminated on both sides. desirable.

It is preferable to coat the vinylidene fluoride / hexafluoropropylene copolymer so that the thickness is 1 to 50 μm. When the thickness is less than 1 μm, coating is difficult, and when the thickness exceeds 50 μm, There is a problem of degrading performance.

Plasticizers for use in the preparation of separator precursors, the group consisting of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethoxyethane, dibutyl phthalate, dimethoxyethane, diethyl carbonate, dimethoxyethane, dipropyl carbonate and mixtures thereof It is preferable that it is any one selected from.

These plasticizers enable the formation of pores without the extraction process by the organic solvent, and also by using the electrolyte component as a plasticizer to reach the chemical equilibrium during the injection of the electrolyte to express the battery performance.

In addition, the inorganic filler and the coating solvent is not particularly limited as long as it is a material commonly used in the technical field to which the present invention belongs, for example, silica and alumina may be used as the inorganic filler, and as the coating solvent N-methyl-2-pyrrolidone, acetone or mixtures thereof can be used.

4. Preparation of Battery Precursors

The battery precursor is prepared by laminating the separator precursor prepared above to be positioned between the anode precursor and the cathode precursor, or laminating in order of the cathode precursor, the separator precursor, the anode precursor, the separator precursor, and the cathode precursor, followed by heating or pressing. Methods and conditions of heating or pressurization are in accordance with methods and conditions well known to those skilled in the art.

5. Activation Step

The activation step is completed by injecting an electrolyte solution containing a non-aqueous organic solvent and an inorganic salt into the unit cell precursor in the electrode assembly. This activated cell is charged by an external energy source before use.

In the present invention, the plasticizer used in the production of the separator precursor is dispersed in the separator precursor in a liquid state. Since the plasticizer dispersed in the liquid state is the same organic liquid as the solvent used in the electrolyte, the plasticizer dispersed in the separator precursor in the liquid state is mixed with the electrolyte solution, so that the electrolyte solution can be impregnated into the separator precursor without any special process. will be.

The non-aqueous organic solvent and the inorganic salt contained in the electrolyte are not particularly limited as long as they are commonly used as the use in the technical field to which the present invention belongs. At least one solvent selected from butyrolactone, 1,3-dioxolane, dimethoxyethane, dimethyl carbonate, diethyl carbonate, tetrahydrofuran, dimethyl sulfoxide and polyethylene glycol dimethyl ether may be used, and a separator precursor may be prepared. It is preferable to use the same plasticizer used in the case. In addition, as an inorganic salt, the lithium compound which dissociates in a solvent and produces | generates lithium ion can be used. Specific examples of the inorganic salts include lithium perchlorate (LiClO ₄ ), lithium tetrafluoroborate (LiBF ₄ ), lithium hexafluorophosphate (LiPF ₆ ), and lithium trifluoromethansulfonate (LiCF _3). SO ₃ ) and lithium bistrifluoromethansulfonylamide.LiN (CF ₃ SO ₂ ) ₂ ).

Hereinafter, the present invention will be described in more detail with reference to Examples. However, it is a matter of course that the scope of the present invention is not limited to the following examples.

Example

600 ml of acetone (Samjeon Chemical) and 65 g of Kinar 2801 (VdF 88wt / HFP 22wt copolymer) (Elf-Atochem) were mixed and stirred for 2 hours in a ball mill to prepare a solution, followed by mesocarbon in the solution. 415 g of Fiber (MCF) (Petoca) and 20 g of Super-P (MMM.Carbon) were added and stirred with a ball mill for 5 hours. 200 mL of ethanol was added to the solution and stirred for 24 hours to prepare an anode composition.

The anode composition was coated on a Cu current collector and then dried at 30 ° C. to prepare a porous anode precursor.

Separately, 600 ml of acetone (Samjeon Chemical) and 50 g of Kinar 2801 (Kdnar 2801) (VdF 88wt / HFP 22wt copolymer) (Elf-Atochem) were mixed and stirred for 2 hours to prepare a solution. 410 g of LiCoO ₂ (Nippon Chem.) And 40 g of Super-P (MMM.Carbon) were further added and stirred for 5 hours with a ball mill. To this solution was added 200 ml of ethanol and stirred for 24 hours to prepare a cathode composition.

The cathode composition was coated on an Al current collector and then dried at 30 ° C. to prepare a porous cathode precursor.

Subsequently, 6 g of Kynar 2801 (VdF 88 wt / HFP 22 wt copolymer), 8 g of dibutyl phthalate (Aldrich) and 6 g of silica (Carbot) were mixed with 50 ml of acetone (trielectrochemical) and ball milled for 6 hours. After stirring to prepare a slurry, the slurry was coated on both sides of a porous polyethylene film (Cellgard) having a thickness of 25 ㎛ and dried at room temperature to prepare a separator precursor.

An anode precursor, a cathode precursor, and a separator precursor prepared as described above were stacked in a bicell structure and laminated at 145 ° C. to prepare a battery precursor.

Thereafter, the obtained battery precursor was dried under vacuum conditions at a temperature of 100 ° C. for 1 hour, and then lithium 2 was injected by injecting an electrolyte solution (1.15M LiPF ₆ in EC: DMC: DEC = 1: 1: 2) under an argon gas atmosphere. The primary battery was completed.

The battery prepared as described above was formed in a charge capacity of 160.5 mAh, and then discharge capacity and high rate characteristics were measured and shown in Table 1 below.

Comparative example

65 g of mesocarbon fiber (MCF) (Petoca), 10 g of Kynar 2801 (Kdnar 2801) (22 wt copolymer of VdF 88 wt / HFP), 9.25 g of Super-P (MMM.Carbon), dibutyl phthalate (Aldrich) 21.75 An anode composition was prepared by mixing g and 700 ml of acetone (Samjeon Chemical).

The anode composition was coated on a Cu current collector and then dried at 30 ° C. to prepare a porous anode precursor.

Separately, 65 g of LiCoO ₂ (Nippon Chemical), 10 g of Kynar 2801 (22 wt copolymer of VdF 88 wt / HFP), 6.5 g of Super-P (MMM.Carbon), 1 g of dibutyl phthalate (Aldrich) 18.5 g and acetone 900 ml were mixed to prepare a cathode composition.

The cathode composition was coated on an Al current collector and then dried at 30 ° C. to prepare a porous cathode precursor.

Prepare a composition for forming a separator by mixing 32 g of Kinar 2801 (22 wt copolymer of VdF 88 wt / HFP), 26 g of silica (Carbot), 42 g of dibutyl phthalate (Aldrich), and 300 ml of acetone (trielectric chemistry). It was. The separator precursor was prepared by casting the separator composition on a polyethylene terephthalate support, drying at 30 ° C., and then removing the film from the support.

An anode precursor, a cathode precursor, and a separator precursor prepared as described above were stacked in a bicell structure and laminated at 145 ° C. to prepare a battery precursor.

Thereafter, the obtained battery precursor was dried under vacuum conditions at a temperature of 100 ° C. for 1 hour, and then lithium 2 was injected by injecting an electrolyte solution (1.15M LiPF ₆ in EC: DMC: DEC = 1: 1: 2) under an argon gas atmosphere. The primary battery was completed.

The battery prepared as described above was formed in a charge capacity of 160.5 mAh, and then discharge capacity and high rate characteristics were measured and shown in Table 1 below.

Formation Standard discharge High rate characteristics Charge capacity Discharge capacity Reversible capacity 0.2C 0.5C 1C 2C Example 160.5 mAh 124.0 mAh 77.3 113.6 mAh 106.1 mAh 98.6 mAh 65.0 mAh Comparative example 160.5 mAh 130.2 mAh 81.1 120.5 mAh 110.2 mAh 97.5 mAh 84.2 mAh

As shown in Table 1 above, the results measured in the battery of the Example prepared without the plasticizer extraction process by the organic solvent was found to be almost the same as the result measured in the battery of the Comparative Example prepared by the conventional method.

As described above, the method of manufacturing a lithium secondary battery according to the present invention enables the production of a lithium secondary battery without a plasticizer extraction process by an organic solvent, thereby preventing environmental pollution problems caused by the extraction process, and the manufacturing cost of the battery. There is an advantage that can be lowered.

Although described with reference to the embodiment shown in the drawings of the present invention, this is merely exemplary, those skilled in the art will understand that various modifications and equivalent other embodiments are possible therefrom. Therefore, the true technical protection scope of the present invention will be defined by the technical spirit of the appended claims.

Claims (7)

(a) preparing an anode precursor and a cathode precursor by applying an electrode composition including an electrode active material, a polymer binder, a conductive agent, and a casting solvent, and not including a plasticizer, to a current collector; (b) coating a slurry comprising a vinylidene fluoride / hexafluoropropylene copolymer, a plasticizer, an inorganic filler and a coating solvent on both sides of the porous polymer film that is not gelled by the electrolyte solution to prepare a separator precursor; (c) laminating the electrode precursor and the separator precursor to prepare a battery precursor; And (D) a method of manufacturing a lithium secondary battery comprising the step of activating by injecting an electrolyte solution to the battery precursor. The method of claim 1, wherein the battery precursor has a bi-cell structure in which a cathode precursor, a separator precursor, an anode precursor, a separator precursor, and a cathode precursor are sequentially stacked. The method of claim 1, wherein the electrode composition further comprises an alcohol solvent selected from the group consisting of methanol, ethanol, isopropanol and mixtures thereof. The method of manufacturing a lithium secondary battery according to claim 1, wherein the porous polymer film which is not gelled by the electrolyte solution is a porous polyethylene film. The method of manufacturing a lithium secondary battery according to claim 1, wherein the porous polymer film which is not gelled by the electrolyte solution is a porous polyethylene film having a porous polypropylene film laminated on both sides. The method of claim 1, wherein the plasticizer is any one selected from the group consisting of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethoxyethane, dibutyl phthalate, dimethoxyethane, diethyl carbonate, dipropyl carbonate, and mixtures thereof. Method for producing a lithium secondary battery, characterized in that. The method of claim 1, wherein the vinylidene fluoride / hexafluoropropylene copolymer is coated to have a thickness of 1 to 50 μm.